Reduction of pilling of fabrics with ultrasonic energy



United States Patent 01 iice 3,525,653 Patented Aug. 25, 1970 3,525,653 REDUCTION OF PILLING F FABRICS WITH ULTRASONIC ENERGY Geoffrey Windle Manock, Harrogate, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Continuation of application Ser. No. 540,832, Apr. 7, 1966. This application Aug. 13, 1969, Ser. No. 851,153

Int. Cl. B29c 27/08 US. Cl. 15673 4 Claims ABSTRACT OF THE DISCLOSURE Pilling of woven or knit fabrics made from spun yarns containing synthetic fibres is reduced by treating the fabric with an ultrasonic beam in order to attach at least some of the fibres to neighboring fibres at intervals.

REFERENCE TO RELATED APPLICATION This application is a continuation of applicants copending application 'Ser. No. 540,832, filed Apr. 7, 1966, now abandoned.

This invention relates to improved fabrics and to a process for making such fabrics which are woven or knitted from spun yarns containing high tenacity synthetic fibres which cause pilling.

It is known that fabrics containing yarns spun from synthetic fibres, particularly those made from high tenacity synthetic linear polymers such as polyethylene terephthalate, give rise during wear, to an effect known as pilling. Pilling is caused through rubbing or abrasion of the fabric which causes the fibres to form into small balls on the surface of the fabric and which due to their high tenacity and abrasion resistance, are retained on the surface of the fabric giving it an unsightly appearance. We now propose to prevent or reduce pilling by a novel method using ultrasonic energy.

According to our invention we provide a process for eliminating or reducing by at least 50% the phenomenon called pilling in woven or knitted fabrics made from spun yarns containing high tenacity synthetic fibres which are liable to cause pilling, wherein the fabric is treated by one or more ultrasonic beams in order to attach at least some of the synthetic fibres to the same or to other fibresin the spun yarn and thereby to eliminate or reduce said pilling by preventing teasing out and migration of the synthetic fibres to the surface of the fabric during testing or in wear.

We also provide improved woven or knitted fabrics made from spun yarns containing high tenacity synthetic fibres in a construction which gives rise to pilling wherein said pilling is eliminated or reduced in that at least a proportion of the synthetic fibres in the spun yarns have become attached more firmly to other fibres in the spun yarns or fabric by the use of one or more ultrasonic beams so that teasing out of the fibres is eliminated or reduced.

Suitable equipment comprises an ultrasonic head piece and an anvil or strip, roller or bar between which the fabric is passed using a magnetostrictive or piezoelectric transducer for exciting the head. Instead of a head piece or horn and an anvil two head pieces orhorns may be used. When two such head pieces are used they are preferably placed in juxtaposition with the fabric to be treated passing therebetween. When two such heads are used it is preferred that their vibrations are synchronised. We have found that if two such heads are so used pilling in the fabric is reduced and glazing of the fabric is minimised and the fabric appearance is improved compared with the each other are submitted to the ultrasonic effect. The

spacing of the rows may be chosen so that the majority of fibres which give rise to pilling are held at least in one spot along their length in the yarn. This holding is believed to be elfected by a local fusing action caused by the ultrasonic beam, with neighbouring fibres. Alternatively the fibres may be attached to other fibres in a pre-selected pattern using ultrasonic beams, in a process somewhat resembling spot welding in that the beams are allowed to act in very small confined areas or spots in the cloth, according to a selected pattern. Suitable devices such as are used on sewing machines for embroidery work may be used to obtain a symmetrical or a'random pattern where the ultrasonic beams are allowed to effect attachment of the fibres.

Preferably the beam or beams are arranged to be emitted from a head or horn which is in the form of a strip at its tip so that the entire width of the fabric may be simultaneously treated across its width, using for example a rotating roller as the anvil or two heads in strip form at opposite sides of the fabric. Strips as wide as 6" are known to be operated by one transducer. If wider strips are used several transducers mounted along their length are required.

A relay circuit may be used to interrupt power whenever the head and the anvil touch, for example when running 01f a finished length of fabric. The electric power used for generating the ultrasonic beams may be controlled by a micro-switch which is held in the on position by the fabric entering the apparatus or alternatively there may be manual or foot control.

A feed and delivery system of rollers may be incorporated to provide suitable passage of the fabric through the apparatus. The head may be spring loaded and may have various shapes to suit various requirements such as a shape of a chisel, a round tip, a wheel, a bar or a spherical or other convex shape.

The complete head may be released by a suitable control and can be lifted to clear the fabric before re-engaging it in another area.

An amplifier may be used to provide the power for the magnetostrictive or piezoelectric transducer at a suittable frequency such as 20 kilo cycles. A suitable device may be included to vary the level of output of power as required.

A suitable frequency range is 10 to 50 kilo cycles but preferably more than 18 'kilo cycles should be used since on a frequency below 15 kilo cycles the process is too noisy for use without eai protection for the operator. The power supplied to each head is 100 to 250 watts per inch Width of fabric to be treated.

A suitable gap between the head and anvil or between heads in juxtaposition varies between to 50% of the fabric thickness. In practice speeds of fabric of 10 to 60 cm. per sec. are most suitable. We have found that fabrics showing at least 4 pills per sq. inch when tested have the number of pills per sq. inch reduced by at least 50% after the treatment. Fabrics having 3 or less pills per square inch on test have the pilling tendency eliminated by the treatment. It should be appreciated that not only is cooling of the transformer essential but the temperature of the head, should not be allowed to approach frequency of 20 kilo cycles, higher frequencies requiring shorter horns. Suitable material from which the horns are made comprise silver steel.

By having two magnetostrictive transducers working in synchronisation and in juxtaposition the maximum effect of the beam will be concentrated at the centre of the fabric without causing any appreciable attachment of the fibres at either surface, thereby unexpectedly avoiding deterioration in the surface properties of the fabric and its handle.

The following example illustrates but does not limit our invention.

EXAMPLE A woven twill fabric made from cotton-spun yarn containing 67% polyethylene terephthalate crimped 2 inch staple fibres and 33% viscose rayon with 60 ends per inch and 55 picks per inch is subjected to a pilling test, wherein samples of the fabric are wrapped round 5 inch tubes of 1 inch diameter and tumbled in a cuboid cork-lined box of 9 inches side length for 5 hours. The average number of pills per sq. inch are counted after removal of the fabric from the tube and it is found that the fabric after tumbling shows 1 to 7 pills per sq. inch depending on the severity offabric cropping. Samples of the fabric were treated between two synchronised heads by an ultrasonic beam using an apparatus which was assembled with the two heads or horns in juxtaposition, each horn being activated by a magnetostrictive transducer powered by a suitable current transformed from the mains to 7 amps at 26 volts, having 20,000 sinusoidal vibrations per second, the current for each transducer and horn being synchronised and coming from separate power units of known construction, each horn about 5.2 in. long of tapering rectangular cross-section 1 x 1 inch had two parallel sides and two concave sides which tapered on a convex curve along their length to a tip having an area of 1 inch x 7 inch at the tip of each horn.

The horns or heads were adjusted to have a gap of 80% of the fabric thickness. The fabric thickness being measured as described in British Standard Test (The Thickness of Textile Fabrics) BS 2544/1954. The fabric was passed between the horns at a speed of 1 ft. per second. In this way 1 inch bands of fabric were treated along the length and repeat parallel rows were made until the entire fabric width had been treated.

Pilling in the treated fabrics is reduced as is set out in the following table.

Pills per square inch Percent reduction in pllling What is claimed is:

1. A process for eliminating or reducing pilling by at least in woven or knitted fabric made from spun yarns containing high tenacity polyethylene terephthalate fibers comprising: passing the fabric between two juxtapositioned head pieces of a ultrasonic beam generator and attaching at least some of the synthetic fibres to the same or other fibres in the spun yarn by means of ultrasonic beams concentrated at center of the fabric and produced by vibrating the head pieces in synchronization thereby avoiding glazing of the fabric and deterioration of handle while eliminating or reducng the tendency of the fabric to pill by preventing teasing out and migration of the polyethylene terephthalate fibres to the surface during subsequent use.

2. A process as in claim 1 wherein narrow, spacedapart rows of the fabric are submitted to the ultrasonic beam.

3. A process as in claim 1 wherein the ultrasonic beam is vibrated at a frequency range of at least 19 kc./s. up to 50 kc./s.

4. A process according to claim 1 wherein narrow rows of the fabric are submitted to at least one ultrasonic beam vibrating at a frequency range of at least 19 kc./s. up to 50 kc./s., the rows being at right angles to each other and so arranged that the majority of fibres which give rise to pilling are held at least in one spot along their length in the yarn.

References Cited UNITED STATES PATENTS 3,053,609 9/1962 Miller.

3,184,354 5/1965 Strother 156-73 3,392,219 7/1968 Smith et al 15673 X FOREIGN PATENTS 1,018,971 2/1966 Great Britain.

OTHER REFERENCES High Frequency Bonding, Parts 1 & 2, Plastics Technology, March 1964.

ROBERT F. BURNETT, Primary Examiner R. O. LINKER, JR., Assistant Examiner US. Cl. X.R. 26-1; 161-150 

